Nearly all brown pelican eggs collected from 13 colonies in South Carolina, Florida, and California in 1969 and from 17 colonies in South Carolina and Florida in 1970 exhibited eggshell thinning. Of the 100 eggs analyzed for residues of pollutants, all eggs contained measurable quantities of DDE; most eggs contained measurable quantities of p,p'-DDD, p,p'-DDT, dieldrin, or PCB's (polychlorinated biphenyls). All eggs contained measurable quantities of mercury. DDE appears to have been responsible for virtually all the eggshell thinning. There is strong evidence that DDE played a major role in lowered reproductive success in South Carolina and California, and this pollutant appears to be intimately related to the population decline in South Carolina. Other pollutants, particularly dieldrin, may have had deleterious effect on reproductive success in South Carolina. Carcasses of pelicans collected by shooting in Florida and South Carolina in 1970 varied in residue load according to age and geographic location. Birds under 1 year of age contained smaller quantities of residues than did birds I year or older.
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Relations of the brown pelican to certain environmental pollutants